1. Technical Field:
The present invention relates to an improvement of a fuel filter contained in a fuel tank, more particularly to a fuel filter contained in a fuel tank which is improved in permeability without deteriorating its foreign matter catching ability.
2. Prior Art:
There are various kinds of fuel filters for catching foreign matters in fuel, of which the fuel filter provided in a fuel tank in such a way as to be soaked in fuel is known.
Japanese Utility Model Laid-Open Publication No. 62-179387 and No. 63-181408 disclose a double filter cloth.
Japanese Utility Model Laid-Open Publication No. 62-179387 also discloses the filter cloth either side of which is formed of a mesh having high wettability and further discloses a fuel suction pipe 15 formed of a mesh of high wettability and a mesh portion 14 provided outside the fuel suction pipe 15 in FIG. 1. Since the fuel suction pipe 15 is formed of the mesh having high wettability, fuel is sucked thereby with certainty even if the liquid level is lowered.
Japanese Utility Model Laid-Open Publication No. 63-181408 also discloses a mechanism having a main nylon filter 38 and an auxiliary stainless filter 46 wherein a large gap is defined between the main filter 38 positioned inside and the auxiliary filter 46 positioned outside.
The known fuel tank contained in a fuel tank has a structure as illustrated in FIGS. 4 and 5. That is, a fuel filter 1 is composed of a filter cloth 2, a frame body 4 for supporting the filter cloth 2 so as to partition and form inner spaces 3 thereof and an outlet pipe portion 5 for discharging the fuel.
The filter cloth 2 used for the fuel filter 1 contained in a fuel tank is required to have the following functions.
Firstly, the mesh size of the filter cloth 2 should be small and accurately fixed so as to catch foreign matters since the primary purpose of the fuel filter 1 is to catch the foreign matters in the fuel. It ranges practically from 100 .mu.m to 60 .mu.m since too small meshes cause filter obstruction.
Secondly, even when the fuel in the fuel tank is at so low level that a part of the filter cloth 2 is exposed above the surface of the fuel and contacts air, air does not pass through the part of the filter cloth 2 contacting the air but fuel alone passes through the same part. For this purpose, the filter cloth 2 should always contain the fuel (in a wet state) at the portion which contacts the air. That is, air can not pass through the part of the filter cloth 2 even if the latter contacts the former at a part of the latter since the passing resistance of air which passes the filter cloth 2 which is moistened with fuel is larger than that of fuel which passes the part of the filter cloth 2 which is soaked in the fuel. In order to always keep the filter cloth 2 wet, the filter cloth 2 should have a structure which is excellent in permeability and should be composed of material which is excellent in permeability, and moreover it should have a structure and a shape which are favorable for capillarity since the permeation of fuel occurs due to capillarity.
As described above, the filter cloth 2 of the fuel filter 1 should be designed considering both of the foreign matter catching ability and the fuel permeability.
On the other hand, the weaving methods of the filter cloth 2 of the fuel filter 1 can be roughly classified into two, i.e., a plain weave as illustrated in FIG. 6 and a tatami-facing-like weave as illustrated in FIG. 7.
Referring to FIG. 6, the plain weave is formed by weaving a warp yarn 5 and a weft yarn 6 alternately one by one at regular intervals H so as to form square meshes M therebetween.
Referring to FIG. 7, the tatami-facing-like weave is formed by linearly putting weft yarns 6 at regular intervals H and alternately weaving the warp yarns 5 into the weft yarns 6 without any interval between the warp yarns 5 (which contact each other) so as to not to form the mesh. (Although no mesh is seen in a plan view, there are gaps between the vertically waving warp yarns 5 and the weft yarns 6, the gaps substantially serving as meshes M.
There are twill weave, sateen weave, etc. which are similar in structure to the plain weave. The twill weave is formed by weaving a pair of warp yarns and a pair of weft yarns alternately at regular intervals so as to form square meshes therebetween, while the sateen weave is formed by weaving the pairs of warp and weft yarns at regular intervals so as to form meshes therebetween, in which a yarn is staggered at an interval of four yarns. Both of these twill weave and sateen weave can be considered to have structures similar to that of the plain weave from the viewpoint of permeability. The plain weave, the twill weave, the sateen weave, etc. will be generally called hereinafter as a plain weave etc.
Filter cloths of tatami-facing-like weave are not in general use recently since the mesh size M can hardly be made fixed and is difficult to be made less than 100 .mu.m.
On the other hand, filter cloths 2 of the plain weave etc. are in general use recently since the mesh size M thereof can be easily made fixed.
The filter cloth 2 of the plain weave etc. in the known fuel filter 1 set forth above, however, has the following problems.
The filter cloth 2 of the plain weave etc. is liable to be insufficient in the capillary permeation of fuel, so that the permeability is lowered to thereby permit the air to pass therethrough.
As described above, although the filter cloth of the tatami-facing-like weave which is excellent in fuel permeability can avoid this trouble, the mesh size M thereof is hardly fixed and moreover it is difficult to range from 100 .mu.m to 60 .mu.m.
Accordingly, it is an object of the present invention to improve the problems of the conventionally known fuel filter contained in a fuel tank and provide a fuel filter contained in a fuel tank having a filter cloth which is improved in the permeability of fuel without deteriorating the foreign matter catching ability.